What does "crus" mean?

Crus: (a) That part of the hind limb between the femur, or thigh, and the ankle, or tarsus; the shank. (b) Often applied, especially in the plural, to parts which are supposed to resemble a pair of legs; as, the crura of the diaphragm, a pair of muscles attached to it; crura cerebri, two bundles of nerve fibers in the base of the brain, connecting the medulla and the forebrain.